A structure having a fine concavo-convex structure on the surface is known to exhibit antireflection performance based on a continuous change in the refractive index. Furthermore, a fine concavo-convex structure is also capable of exhibiting super-water-repellent performance as a result of the lotus effect.
In order for a fine concavo-convex structure to exhibit satisfactory antireflection performance, the interval between adjoining convexities or concavities needs to be smaller than or equal to the wavelength of visible light. Regarding the method for producing a structure having such a fine concavo-convex structure on the surface, for example, a so-called nanoimprint method including the following steps (i) to (iii) is known:
(i) a step of interposing an active energy ray-curable resin composition between a substrate and a mold having a reverse structure of a fine concavo-convex structure on the surface;
(ii) a step of irradiating the active energy ray-curable resin composition with active energy rays such as ultraviolet radiation, and thereby curing the active energy ray-curable resin composition; and
(iii) a step of separating the cured product and the mold.
However, a structure having a fine concavo-convex structure on the surface has poor scratch resistance compared to a structure having a hard coat layer with a smooth surface, which has been produced from the same material as the material forming the fine concavo-convex structure. Thus, such a structure having a fine concavo-convex structure on the surface has a problem that the antireflection performance is easily deteriorated because the protrusions having a size in the order of nanometers are susceptible to damage, or because the protrusions wear out when the operation of wiping off the dirt adhered to the surface is repeatedly conducted.
Regarding the method of enhancing the scratch resistance of a structure having a fine concavo-convex structure on the surface, a method of incorporating a lubricating agent into the material that forms the fine concavo-convex structure to make the surface slippery, and thereby preventing the protrusions having a size in the order of nanometers from being damaged, may be mentioned.
However, lubricating agents often bleed out to the structure surfaces, and thereby cause a problem that the reflectance of the surface or the haze value is increased, and the antireflection performance is deteriorated.
Furthermore, a method of imparting resilience to the protrusions having a size in the order of nanometers by using a flexible resin composition for the formation of the fine concavo-convex structure, and turning aside any burden, has also been suggested (Patent Document 1).
However, as in the case of Patent Document 1, when resilience is imparted to the protrusions having a size in the order of nanometers, the surface is prone to become sticky so that the friction force is increased, and strong force is required to wipe off dirt. Furthermore, when dirt is wiped off with strong force, the protrusions having a size in the order of nanometers are easily damaged, and cause a problem that leads to deterioration of the antireflection performance.